Field of the Invention
The present invention relates to a coil component, and more particularly relates to a coil component using a drum core.
Description of Related Art
A coil component using a drum core can be surface-mounted on a printed circuit board differently from a coil component using a toroidal core, and thus has been widely used for mobile electronic devices such as a smartphone. Further, because the coil component using a drum core has a low height, it also contributes to thinning of mobile electronic devices.
However, in recent years, further thinning of mobile electronic devices has been desired, and in order to realize this, a further lower height has been desired for the coil component using a drum core. As one method of realizing a low height of a coil component, a method in which a magnetic top plate generally bonded to a drum core is omitted can be considered. However, in this case, because leakage of the magnetic flux increases, other circuits such as an antenna may be adversely affected. Meanwhile, because a magnetic top plate made of ferrite is fragile, if the thickness thereof is reduced, its strength becomes insufficient, and thus the magnetic top plate may be broken at the time of assembly or at the time of actual use.
To solve the above problems, it suffices to use magnetic-powder containing resin having flexibility instead of using ferrite as a material of the magnetic top plate. The magnetic-powder containing resin can maintain certain strength even if it is thinned. Therefore, by using the magnetic-powder containing resin as the material of the magnetic top plate, leakage of the magnetic flux can be suppressed while realizing a low height. As an example of using magnetic-powder containing resin as a material of a magnetic top plate, coil components described in Japanese Patent Application Laid-open No. H9-219318 and Japanese Patent Application Laid-open No. 2004-363178 can be mentioned.
Magnetic-powder containing resin can be produced by applying a mixed solution in which magnetic powder is mixed in binder resin to a base material such as abase film. However, in the mixed solution applied to the base film, distribution of the binder resin and the magnetic powder is not uniform, and a region containing binder resin in high density and a region containing magnetic powder in high density may be generated depending on the conditions. Particularly, a surface layer part on the base film side and a surface layer part on the opposite side thereof may contain the binder resin and the magnetic powder in different densities from each other.
In this manner, because the front and back sides of a magnetic top plate made of magnetic-powder containing resin may have different characteristics from each other, at the time of bonding the magnetic top plate to a drum core, the obtained characteristics and functions may differ according to which side of the magnetic top plate is bonded to the drum core.